The present invention relates to a roof assembly for an electric arc furnace used for melting metals, and has particular application in a roof assembly of the type consisting of inner and outer support rings, a ring for containment of a refractory electrode-delta center, and a number of water-cooled roof segments or panel units circularly arranged to have their sides adjacent each other between the two support rings.
Past designs for a roof of an electric arc furnace having water-cooled segments or panel units included at least two types: an overhead support structure for suspending the panel units as taught in U.S. Pat. No. 4,216, 348; or an arrangement where the panel units are designed to abut each other to be self-supporting as disclosed in U.S. Pat. No. 4,021,603.
There are several disadvantages associated with both types. In the first design, i.e. U.S. Pat. No. 4,216,348, radial support beams in the overhead support structure interfer with the easy insertion and removal of the roof panels since handling of the panels from above the roof assembly is desirable. Consequently, disassembling of one or more of the radial beams was necessary. In addition, and aside from the substantial added costs the overhead support structure adds a substantial amount of weight to the roof assembly, which, in the case of cast metal roof segments, this additional weight can be prohibitive.
The design in U.S. Pat. No. 4,021,603, for the most part, does not have the problems previously mentioned with regard to U.S. Pat. No. 4,216,348 patented overhead suspension design. However, this design also has serious disadvantages.
First, proper sizing and close tolerance of the segments and outer ring is mandatory. Since abutment of each roof segment relative to each adjacent one and their containment in the outer ring provide for the self-supporting feature of the roof assembly, the manufacturing of these segments require very close tolerances in order to achieve proper assemblage and support thereof. Oversizing or undersizing of any one or more of the segments or the outer ring may interfer with the object of the self-supporting aspect. Maintenance of this design presents other problems. To remove a single roof segment for repair or replacement, removal of the refractory electrode center is required since the assembled segments support the refractory center. In addition, the assembled remaining segments must be kept in their initial refractory supporting position. Otherwise, the entire roof assembly has to be removed from the furnace for the repositioning of the segments.
A third problem with regard to the U.S. Pat. No. 4,021,603 design still involves the abutting relationship of the assembled roof segments relative to each other. In high and ultrahigh power furnaces, this abutting relationship can be disrupted due to the substantial amount of expansion and contraction of the panels caused by the extreme thermal variations in the furnace. The results may invariably be distortion or failure of some or all the segments and perhaps a total collapse of the roof.
Inherent in each of the two above roof designs is the likelihood of the accumulation of debris on the top of the assembled roof.
The above disadvantages and limitations of the roof assembly designs are overcome by the features of the present invention.